In addition to having an empty lot already on the map that is at least the size of the one you are trying to place, the commercial lot types have to match. You cannot, for example, place a pre-made Arcade (ie, bowling alley) onto an empty lot typed as a Dance Club.
Does that help or have you already made sure that the commercial lot types match?
Well thanks.. sounds like a lot of trial and error and cheats I never use but I'll give it a shot when I feel more ambitious and have several hours to play around with my edit world stuff. Does this work all the time when you can **** out the guesimated number of value in the brackets?
Stormkeep
A solution for lots sinking or going really high is in this thread: http://forum.thesims3.com/jforum/posts/list/378588.page. You want to read the 2nd to last post in the thread.
1. Not since the latest patch and EP.. that is broken, snubbing furniture up to the wall or in the quartertile squares that you used to be able to use for years no longer works. It's a new bug already reported and hopefully soon fixed.